Varying titers of neutralizing antibodies to streptococcal superantigens in different preparations of normal polyspecific immunoglobulin G: Implications for therapeutic efficacy

In as much as normal intravenous polyspecific immunoglobulin G (IVIG) neutralizes the activity of a wide spectrum of superantigens, it may be an efficient adjunctive therapy for diseases associated with superantigen- producing organisms, including severe group A streptococcal diseases. The neutralizing activity against purified superantigens, streptococcal pyrogenic exotoxin.s (Spe), and a mixture of superantigens present in culture supernatant of clinical group A streptococcal isolates was determined for five IVIG preparations. A significant variation among different IVIG preparations (P < .05) and different lots of the same IVIG brand (P < .044) was found. Neutralization of SpeA activity was significantly lower than that of other streptococcal superantigens (P < .05); however, there was no correlation between SpeA binding and SpeA neutralizing activity in different IVIGs. Plasma samples obtained from patients after IVIG infusion varied in their titers of neutralizing antibodies to culture supernatants prepared from their respective isolates, and this variation paralleled differences in the neutralizing titer of the IVIG lot administered to each patient studied. The study suggests that complete neutralizing activity may be achieved by optimizing the type and/or dose of IVIG used in treatment.